Abstract
Backscatter communication is an emerging paradigm for pervasive connectivity of low-power communication devices. Wirelessly powered backscattering wireless sensor networks (WSNs) become particularly important to meet the upcoming era of the Internet of Things (IoT), which requires the massive deployment of self-sustainable and maintenance-free low-cost sensing and communication devices. This article will introduce the state-of-the-art antenna design and radio frequency (RF) system integration for wirelessly powered backscatter communications, covering both the node and the base unit. We capture the latest development in ultralow-power RF front ends and coding schemes for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> -level backscatter modulators, as well as the latest progress in wireless power transfer (WPT) and energy harvesting (EH) techniques. Newly emerged rectenna system, waveform design, and channel optimization are reviewed in light of the opportunities for adaptively optimizing the WPT/EH efficiency for low-power signals with varying conditions. In addition, advanced device packaging and integration technologies in, e.g., additively manufactured RF components and modules for microwave and millimeter-wave ubiquitous sensing and backscattering energy-autonomous RF structures are reported. Inkjet printing for the sustainable and ultralow-cost fabrication of flexible RF devices and sensors will be reviewed to provide a prospective insight into the future packaging of backscatter communications from the chip-level design to complete system integration. Finally, this article will also address the challenges in fully wireless powered backscatter radio networks and discuss the future directions of backscatter communication in terms of “Green IoT” and “Low Carbon” smart home, smart city, smart skin, and machine-to-machine (M2M) applications.
Highlights
Commercial far-field UHF RFID tags can typically be interrogated within a few meters, which inevitably excludes their applications from long-range object tracking and monitoring
We have introduced the latest progress in advanced modulation schemes and hardware realization of ultralowpower backscattering communication devices
Advanced packaging and device fabrication techniques using inkjet printing and additive manufacturing were presented from the chip/device-level design to system-level integration
Summary
Future wireless environments will rely on massive machine-type communications and the Internet of Things (IoT) to enable an increasingly intelligent world. With the aid of the μW-level backscatter communication system, wirelessly powered backscatter communication networks via RF energy are emerging as an innovative solution to revolutionize the research progress of the passive WSNs. In this article, we present the state-of-the-art wireless-powered backscatter communication systems with a specific focus on antenna design, RF system integration, and advanced packaging technologies. This article selectively presents advanced hardware design and coding schemes for ultralow-power, high-rate, and long-range backscatter communications compatible with legacy devices and systems (see Section II). We envision the future generation of joint wireless power and device networks with a massive number of flexible, low-cost, and highly integrated infrastructures (e.g., smart sensors, monitors, and implants) that cooperatively operate in a self-sustainable and intelligently controlled fashion, thereby opening up new opportunities in green IoT, smart home, smart skin, machine-to-machine (M2M), and low-carbon wireless systems. Since the array beams have to be formed toward the readers whose location can only be known by the tags in monostatic systems, several passive retrodirective structures have been developed to cope with
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